Reproduction is a tightly regulated function of an organism that is crucial to the perpetuation of a species. The pituitary gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), play an essential role in the reproductive process to control fertility by directing steroidogenesis and gametogenesis. Befitting their important roles in endocrine physiology, the synthesis and secretion of LH and FSH are under complex regulation by hypothalamic neuropeptide inputs (most notably gonadotropin-releasing hormone, or GnRH) and gonadal sex steroid and peptide hormones. The precisely coordinated integration of these signals leads to appropriate LH and FSH subunit gene expression, protein synthesis, and secretion to promote sexual maturation and control normal reproductive function. With the support of this R01 award, we have identified molecular and cellular mechanisms and pathways by which these factors control gonadotropin gene expression and secretion. We have identified signaling pathways, transcription factors, and cis-regulatory elements by which varying patterns of pulsatile GnRH differentially regulate LH and FSH subunit gene expression using cellular, animal and human models. The overarching goal of this project is to delineate the mechanisms and pathways underlying the carefully orchestrated control of LH and FSH release to allow for reproductive integrity and fertility. We hypothesize that these cellular factors modulate the pathways by which varying GnRH pulse frequencies regulate gonadotropin subunit gene expression to contribute to appropriate regulation of gonadal function, cyclicity and fertility in vivo. Over the next five years, we propose to: (1) generate new mouse models to further translate our cellular studies into the in vivo context; (2) extend our studies of the downstream mechanisms by which the pulsatile GnRH signal is decoded to investigate the role of the Nr4a1 nuclear receptor family we have identified to be highly differentially regulated by varying frequencies of pulsatile GnRH; and (3) test the hypothesis that GnRHR couples differentially to G ? s and G ? q/11 depending on GnRHR numbers, serving as the gonadotrope GnRH pulse frequency decoder to result in subsequent differential regulation of LH and FSH. We are in a unique position to take advantage of our perifusion system combined with our molecular and cellular biology expertise in parallel with our experience in mouse genetics and physiology to successfully perform the proposed studies. The successful completion of these aims is expected to provide insight into the mechanisms by which gonadotropes decode GnRH pulse frequency to differentially regulate LH and FSH, critical for physiologic control of reproduction and fertility. The elucidation of these pathways will generate new potential therapeutic targets for treatment of infertility, precocious or delayed puberty, hypothalamic amenorrhea, and polycystic ovarian syndrome. The results obtained from this research will therefore have a significant impact on the field of reproductive medicine.